Freight loading docks are usually built to a more or less standard height to cooperate with commercial trucks, trailers, and railroad freight cars. A dockboard or dockplate is used as a ramp to bridge the gap and sometimes the tolerable difference in level between the dock and vehicle bed, to facilitate the passage of handtrucks or forklift trucks that are used to load and unload freight between the dock and the beds of such different kinds of freight carrying vehicles. The ramp or bridge is usually present in the form of a dockboard or dockplate of sufficient length and width to first bridge the gap between the edge of the dock and the vehicle bed and secondly to provide a dockboard with a convenient slope for a loading truck to move up and down when the respective levels of the dock and the vehicle bed are not substantially coplanar. Sometimes permanent dockboards are hinged to the dock and the free edge is raised and lowered by power driven means to meet a truck bed. Such permanent installations are very expensive and, of course, serve only one doorway.
More frequently for warehousing and conventional freight loading uses, portable dockboards are needed that can be moved, for example, either to meet incoming trucks or from one location to another on the loading dock as various shipments are handled through various doorways or to and from various warehouse zones. Simple dockplates are sometimes used to serve as such portable bridge means but in order to produce larger portable and relatively lighter weight structures that are adapted to accommodate heavier loads and to provide safer ramps, the preferred dockboard is provided with a beam like configuration and for this purpose has side rails integral with the edges of the generally flat bridge element. These side rails, which function as stiffening means for the flat surface, may vary in height from 21/2 inches to as high as 4 inches or more depending upon the load for which the ramp is designed.
The smaller dockboards and by far the majority of those boards on the docks today are designed to be manually dragged or carried from one location to another. Much less frequently, portable dockboards are provided with means for the attachment of a chain to the board in such a manner that the chain is used as a sling to hang on the forks of a forktruck so that the dockboard can be carried on the forktruck from place to place. However, the attachment of a chain to the board presents problems and labor is required to secure the chain and assist in placing the chain loop on the forks of a forktruck. When the board is lifted by the forks, there is more or less tilting of the dockboard that may cause some inconvenience during the move and ultimate placement of the dockboard after it has been moved into place. When the dockboard has been transported to a new location and is in place, the chains must be unhooked and stored out of the way before the ramp can be used.
Another procedure that has sometimes been used in the past to mount the dockboard on a forklift truck to be transported, involves raising a corner or edge of the board either manually or with a crowbar, high enough to permit the forks of a forktruck to be driven under the raised edge. This requires the presence of a strong laborer to perform the heavy lifting effort with obvious limitations of the weight that can be raised when a manual effort is used. When crowbars are provided, a manual effort must be exerted with the exercise of some skill to raise a corner. Not infrequently, the crowbars disappear or are not readily available at the site where they are needed and time is lost while the tools are procured.
Attempts have been made to partially mechanize the movement of ramps as shown in the U.S. Pat. Nos. to Whiteman, 2,597,213, May 20, 1952 and to Ambli, 3,122,764, Mar. 3, 1964.
It is to be noted that Ambli is an example of the permanently attached type of ramp that is operatively mounted at a single loading station and his bridge element is not adapted to be transported from place to place.
The Whiteman patent discloses a portable dockboard, or as he calls it, gangplank, for a loading dock. This prior art invention makes use of two wheels adapted to turn the ramp into a trundle so that an operator may balance the board on the axle between the wheels disposed on the opposite sides of the board and manually roll the board from place to place on the dock. This manually manipulated board must necessarily be a relatively lightweight construction when compared with a dockboard designed to be transported on a forklift truck. The axle of the manually transportable Whiteman trundle is made in the form of a shaft passing under a hump at its middle section. The shaft includes bracket arms for the wheels. The bracket arms are integral with the axle for simultaneous movement upon operation of a handle means. The wheel mounting arrangement is designed to have the board balanced on the wheels to permit the board to be rolled from place to place and the entire dead weight of the board must be elevated and balanced during such movement. Because of the presence of the hump formed at the midpoint along the length of the board movement of handtrucks particularly, and even forktrucks to some extent over the hump during loading and unloading, is rendered more difficult. Either because of the difficulty involved in trundling the Whiteman dockboard from place to place or because of the hump construction, insofar as is known to the present applicant, the Whiteman structure has not found favor in industrial uses.